The present invention relates to a channel data extracting circuit and extracting method for extracting data from a byte-multiplexed frame for each channel in SDH (Synchronous Digital Hierarchy).
Conventional SDH data multiplexing formats include STM (Synchronous Transfer Module)-1 (bit rate: 150 Mbps), STM-4 (600 Mbps), and STM-16 (2.4 Gbps). These multiplexing formats cannot efficiently use a transmission channel in containing packet data such as PPP (Point to Point Protocol).
Virtual concatenation, which is a technique for solving this problem, can assign to an SDH channel an arbitrary band (VC (Virtual Container)-3 (50 Mbps)×n, VC-4 (150 Mbps)×n). For example, in STM-16, 48 VC-3 are multiplexed, and the channel band can be set with intervals of 50 Mbps from VC-3×1 (50 Mbps) to VC-3×48 (2.4 Gbps) by virtual concatenation.
Arbitrarily setting a channel band enables efficient use of the channel such that the band utilization factor is 66% in mapping using VC-4, but 100% in mapping using two channels of VC-3 when 100-Mbps Ethernet data is contained in SDH.
SDH is constituted by sequentially multiplexing the payload bytes of a frame. In general, an n→1 selector is used to extract data from a byte-multiplexed frame for each channel or for each channel by virtual concatenation. However, if the channel data extracting circuit for extracting data for each channel is formed using the n→1 selector, the hardware becomes bulky.